Preschool and homework?

When two weeks ago my son's new teacher told us that they are going to get homework I was a little bit in a shock... I thought he is only 4 and a half years old, he spends seven hours a day in school. When he comes home he needs to play, be with his sister, mommy and daddy who he misses all day. He does not need to learn at home too.
In the first two weeks I realized that these homeworks are not such a big deal, the most of them are coloring pages, line tracing, but we had to found words with "i" in a rhyme yesterday - that was little bit of a challenge.
I do not really know what to think. The first two times it was hard for him - and hard for us too - to get him do it. But today we really had fun. But I still don't know if he really needs it?
When I went to first grade - I was 6 - I didn't know any letters, I didn't know how to read. I know it was almost three decades ago, but it was all right. Nobody expected me to do such things at that early age.
I know that kids these days are smarter than we were at this age. They've got so much more impulse that they just learn faster and more. But does he really need to have homework?